Air logic circuit for airfeed peck drill

ABSTRACT

An improvement to an air logic circuit for an airfeed peck drill includes the insertion of a retract valve between the command valve and the air motor. This retract valve generates a required signal to only allow the drill quill to feed forward after it has been fully retracted

BACKGROUND OF THE INVENTION

The present invention relates to airfeed tools, more particularly thepresent invention relates to air logic circuits for airfeed tools.

The use of peck drilling in heavy industry, particularly industry whichrequires the drilling of a plurality of holes in a variety of metalpieces, has shown a dramatic increase in recent years. This is becausethe holes resulting from a peck drilling operation exhibit greateraccuracy then holes drilled by conventional drilling operations.Additionally, the surface finish of the hole is much smoother thanobtained with conventional drills.

U.S. Pat. No. 4,123,188 to Deremo et al. and U.S. Pat. No. 4,421,441 toHirose are representative of the design of airfeed peck drills. Suchprior art airfeed peck drills include a motor and reduction gearingwhich is contained within a cylinder to form a drill quill which isattached to the end of an air cylinder. The air cylinder in these priorart drills is used to advance and retract the drill quill into an out ofa workpiece. In order to prevent the drill quill from feeding forwardbefore being fully retracted, the back pressure created by the returningquill is used as a signal.

On newer airfeed drills, different sized areas are used on thefeed-retract piston. The air logic circuitry as taught in U.S. Pat. No.4,123,188 will not provide the necessary signal to prevent the tool fromfeeding forward until fully retracted.

There is therefore a need in the art to provide an air logic circuitwhich will prevent airfeed peck drills having different sized areas oneither side of a feed retract piston from feeding forward until fullyretracted.

SUMMARY OF THE INVENTION

An improvement in an air logic circuit for an airfeed peck havingdifferent sized areas on either side of a feed-retract piston preventsforward feed until the quill is fully retracted by incorporating aretract valve between the command valve and the air motor of the airfeedpeck drill. This retract valve is used to sense the full retraction ofthe quill and then generate a signal when the quill has been fullyretracted.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the improvement to the air logic circuit of anairfeed peck drill of the present invention may be had by reference tothe drawings wherein:

FIG. 1 is a perspective view of an airfeed peck drill; and

FIG. 2 is a schematic diagram of the air logic circuit for an airfeedpeck drill.

DESCRIPTION OF THE EMBODIMENTS

An airfeed peck drill 10 of the type incorporating the air logic circuitofthe present invention is shown in FIG. 1. Such tools are characterizedby operating in a pecking fashion. This peck type drilling includes theinsertion, extraction and reinsertion of a rotating drill bit into ahole.It has been found that this manner of drilling a hole provideextremely accurate holes with a very smooth internal surface finishes.These resultsare accomplished because the flutes of the drill are purgedof metal shavings or chips each time the drill is pecked out of the holeand the drill tip is allowed to cool when it is not in contact with thebottom of the hole being drilled.

Air logic circuits are used to control the insertion, extraction andreinsertion of the rotating drill quill 100 into the hole being drilled.In FIG. 2 a schematic diagram of the air logic circuit for an airfeedpeckdrill is shown. In this diagram, the tool is shown in the retractedposition and the main air supply has been disconnected from the tool 10.All valves are shown in their reset position. Each valve is designatedby the name which appears in close proximity to the valve. The smalltriangles represent the main air supply. The letters EX stand forexhaust.Additionally, the circuit includes shutter valves, 20, on-offvalves 30, a flow control 40 and an accumulator 50.

Operation of the tool begins with applying air to the tool whichactivates the INTERLOCK valve. This sends a puff of air to the COMMANDand FEED valves resetting them if necessary. The INTERLOCK valve remainsin a set position while air is supplied to the tool. This set positionis done to ensure that the tool is retracted regardless of what statethe tool was inprior to the last removal of the supply of air from thetool.

Depressing the START BUTTON sets the COMMAND valve which allows air toflowthrough the RETRACT valve to shuttle the FEED valve. The tool isthen allowed to feed forward and the motor begins to run. Air throughthe MOTORvalve sets and maintains the RETRACT valve.

The drill mode chosen determines what happens next. The mode is selectedbythe configuration array of the on-off valves. In the conventional modeof operation, the tool will continue to feed forward until either theDEPTH valve or STOP valve is depressed. The signal from either the DEPTHvalve or the STOP valve shuttles both the COMMAND valve and FEED valveto their reset positions. When in these reset positions the tool iscaused to retract and shut off.

In the dwell mode of operation the tool will feed forward, and if notinterrupted by the STOP valve, it will hit the DEPTH valve. When it hitsthe depth valve, air will be diverted to the TIMER valve. After apredetermined amount of time has elapsed, the TIMER valve will fire andreset the FEED valve and COMMAND valve to send the quill back to thebeginning of its stroke and turn the motor off.

The peck mode of operation is identical to the dwell operation exceptfor two key points. First, the TIMER valve is fed with quill feed air.And secondly when the TIMER valve reaches a preset time, only the FEEDvalve is shuttled and not the COMMAND valve. This means that when thetool is retracted, the MOTOR valve shuts off removing it signal from theRETRACT valve. Air is then fed from the RETRACT valve through the setCOMMAND valve and shuttles the FEED valve to its feed position. The feedand retract action continues until the tool hits the DEPTH valve or theSTOP valve which sends the quill back to the beginning of its stroke andturns the motor off.

The addition of a RETRACT valve between the COMMAND valve and the motorin drill quill 100 allows the circuitry taught in U.S. Pat. No.4,123,188 to be applied to airfeed peck drills wherein the feed andretract piston 90 is characterized by having different areas on eitherside. Without the RETRACT valve, the tool will not feed forward untilfully retracted. Accordingly, when motor supply air is not sensed by theretract valve, thequill will be in its fully retracted condition.

The foregoing embodiment is intended to illustrate the present inventionand not to limit it in spirit or scope.

It is claimed that:
 1. An air logic circuit for controlling the movementof an airfeed peck drill having different sized areas on either side ofa feed-retract piston and including a command valve and an air motor,said air motor being contained within a quill, said circuit comprising:acoupling between the command valve and a source of pressurized air; aretract valve coupled to said command valve and in a series connectionbetween said command valve and the air motor; said retract valveconstructed and arranged to sense air motor supply air pressure, andgenerate a signal when no air pressure is being supplied to the airmotor; whereby the tool will move to its retracted state regardless ofthe state of the tool prior to the last removal of supply air from thetool.